Summary

Modern refrigerator design is aimed not only at energy savings but also at product robustness to evaporator frosting. Whilst the former is evaluated by means of standardized test procedures, the latter is assessed by testing the refrigerator under real usage conditions, when the doors are opened in a regular basis, allowing moisture to enter the refrigerated compartment and, consequently, frost to accumulate on the evaporator surface. As the frost layer grows, the air-side pressure drop rises, reducing the air flow rate and, therefore, the evaporator capacity. As a consequence, the compressor is driven to run longer cycles, thus increasing the energy consumption. The laboratory procedures required for product assessment and development rely on costly and time consuming experiments. Albeit it has been advocated that the adoption of simulation models may aid the product development process, there is no model available in the open literature which is capable of simulating the refrigerator performance under door-opening and frost build-up conditions. Therefore, a mathematical model for simulating the transient behavior of a domestic refrigerator in such conditions has been advanced in this work. A first-principles simulation model was put forward for the refrigeration loop, whereas a semi-empirical approach was adopted for the refrigerated compartment, in such a way that the key empirical parameters were obtained by testing the refrigerator in an environmental chamber. The model was validated against experimental data, when it was found that its predictions for power consumption and refrigerant mass flow rate fell within a ±10% error band, its predictions for accumulated frost mass were within a ±20% error band, and its predictions for compartment air temperatures were within a ±2K error band. The model is also capable of predicting the behavior of some non-measurable variables, such as the time evolution of the liquid-vapor to vapor transition point of the refrigerant in the evaporator, the density and thickness of the frost layer over the different rows of the evaporator and also the contribution of each of these rows on the air side pressure drop on the evaporator.

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